1. Field of the Invention
This invention relates to ultrasonic flowmeters and more particularly to an ultrasonic flowmeter which is suitable for measuring the velocity of flow of a fluid by utilizing a continuous ultrasonic signal, quickly with high accuracy.
2. Description of the Prior Art
A sing around type flowmeter has been well known as an ultrasonic flowmeter using an ultrasonic wave. In the flowmeter, whenever an ultrasonic pulse from the transmitting device reaches the receiving device through a fluid to be measured, the next pulse is applied to the transmitting device, so that its oscillation signal is obtained from the time required for the ultrasonic pulse to propagate in the fluid to be measured, thereby to measure the flow rate of the fluid.
If, with such a flowmeter, the distance between the transmitting device and the receiving device is L, the velocity of flow of a fluid to be measured is V.sub.F, the velocity of sound in the fluid is V.sub.T, the angle formed by the line connecting the transmitting device and the receiving device with respect to the direction of flow of the fluid is .theta., and the sectional area of a conduit in which the fluid flows is A, and if the time T.sub.1 required for a pulse signal, or a pulse signal including the resonance frequency of the transmitting device as the carrier signal, transmitted by the transmitting device to reach the receiving device is measured, then ##EQU1## Therefore, if the value V.sub.F is obtained from the equation (1), then the flow rate U can be obtained from the following equation (2): EQU U=V.sub.F.A (2)
If, upon reception, the transmission signal is emitted again and this operation is repeatedly carried out, then the number of times (n) of signal transmission is reversely proportional to the aforementioned time T.sub.1. According to this fact, signal transmission and reception is repeatedly carried out to average the measurement values. This is the practice employed for the conventional flowmeter to improve the measurement accuracy.
However, the method is still disadvantageous in that, since signal transmission and reception are carried out many times, it takes several seconds to complete the measurement, measurement errors due to the presence of bubbles in the fluid are liable to be accumulated, and measurement errors are liable to be caused because of the deformation of the rise part of the received signal waveform and the irregular fall part of the same.